All memory modules used were OWC memory. The results shown here are with Mac OS X 10.6.7 and the latest Photoshop CS5 12.0.4 64-bit.

Memory clock speed and hence memory bandwidth is one measure of performance, but in the real world with real programs, the on-chip caches often hide memory bandwidth limitations; this varies by task because of the amount and pattern of memory access during computation.

Note: as previously documented, Photoshop CS5 is faster on a 6-core Mac Pro than on a 12-core Mac Pro, this is not new and has nothing to do with the memory, but rather with engineering assumptions that degrade performance.

Lightroom 3.3 Import 128 CR2 RAW files

Import 128 CR2 RAW files, generating 1:1 high-quality previews.

Lightroom 3.3 is not demanding of the amount of memory while importing, and the bandwidth apparently has little effect on the 12-core Mac Pro, most likely because LR3 does a poor job of using all the CPU cores, so the memory bandwidth needs are relatively low, since no more than about half the cores are actually used.

MemoryTester 'compute'

Six modules is optimal, with a clear loss of performance using eight modules. The Mac Pro uses triple channel memory (two channels of 3 modules each), so with eight modules it must drop down to dual-channel bandwidth.